Surface active compounds constitute an exceedingly important class of industrial organic chemicals finding a wide variety of uses, e.g. as detergent for washing purposes, as emulsifiers in food and feed products, or even as functional ingredients in many personal care products as shampoos, moisturing creams etc.
Basically, surfactants are, on the molecular level, characterised by and owe their properties to presence of hydrophobic and hydrophilic regions within the individual surfactant molecules. This particular constellation can be established in numerous fashions, e.g. by combining sulphonic acid residue, a quarternised ammonium entity or a glycerol moiety with an alkyl chain as is the case in the linear alkyl surfactants, the quarternised alkyl amines, and the monoglycosides, respectively. In the actual design of such surfactant molecules major consideration is given to the detailed molecular architecture of the compounds, important issues being the precise balance between the hydrophilic and hydrophobic domains of the surfactant molecules, and the actual special arrangements of these parts of the molecules. Besides, consideration is obviously given to the possibilities of actually producing the surfactants in high yielding processes and on the basis of raw materials available at reasonable costs. The environmental issues related to the eventual loading of the surfactant into the environment are finally a matter of major concern.
Due to these considerations there have over the years been a keen interest in preparing surfactant molecules on the basis of sugars and fatty acids, e.g. as sugar esters. Such conjugates were expected to exhibit surface active properties due to the presence of the hydrophilic sugar regions and the hydrophobic fatty acid residues. The balance, and thus the precise properties of the conjugates, might be varied through changes of the nature of the sugar and the fatty acid residues; the materials would be producable from exceedingly cheap raw materials; and the surfactants, being composed of and degradable into natural constitutents, would not be harmful to the environment.
As a specific example of surfactants, reference is made to Phillip.J.Coconut stud. 5 (1980), 51 et sec., wherein coconut fatty acid esters of methyl glucopyranoside is described. However, there is no mentioning in this paper about these surfactants being used as additives to detergents. As examples of specific commercially us.RTM.d surfactants which are additives to detergents, Berol 065 and Berol 160 (fatty alcohol ethoxylates) manufactured by Berol AB, Sweden, can be mentioned.
Synthesis and production of pure sugar esters by conventional means have, in spite of many attempts, turned out to be quite difficult. This is due, among other things, to the presence of several chemically similar groups in the sugar molecules which, accordingly, are esterified at several positions by exposure to esterification reagents. Sugar esters prepared by chemical means are, therefore, usually mixtures of compounds differing in respect to the degree of esterification and in the positions of the acyl groups on the carbohydrate moiety of the products. Since, in addition, the chemical procedures for chemical esterification turn out to be quite cost intensive, the sugar esters so far made available on an industrial scale find a rather limited use only.
In view of the difficulties encountered in production of sugar esters by chemical means and the attractiveness of these compounds as industrial surfactants, much attention has during the recent years been devoted to the possibility of utilising enzymes for synthesis of the sugar esters. One major rationale behind this interest is that enzymes are known to exhibit a high degree of regio- and enantioselectivity which might be exploited for selective esterification of one or more hydroxy groups in sugar molecules. Cheap starting materials might be utilised in enzymatic processes which might, therefore, lead to low priced sugar esters of a high quality. The enzymes envisioned as catalysts in processes of this kind are primarily lipases which catalyse hydrolysis of ester bonds and which do, therefore, in principle, also catalyse the reverse reaction, i.e. ester synthesis.
The attempts to develop efficient enzymatic syntheses of sugar esters have, however, so far, been unsuccessful. One major reason for this failure is the major polarity difference between the two substrates of the esterification reaction, the sugar and the fatty acid or a derivative thereof, and the necessity of avoiding water in the reaction medium in order to drive the enzymatic reaction in the directions of synthesis. Few good solvents for both sugars and fatty acids or their derivatives are thus available and these solvents will often inactivate enzymes.
These difficulties inherent in enzymatic synthesis of sugar esters are reflected in the cases reported as for example in U.S. patent specification No. 4,614,718 and in J.Am.Chem.Soc. 108 (1986), 5638-5640 and 6421-6422, and 109 (1987), 3977-3981. These publications teach application of lipases for esterification of sorbitol and sorbital with fatty acids, and transesterification from activated esters of free fatty acids onto long chain glycosides with lipases, respectively. The poor yields, the low selectivity of the reactions and the toxicity of solvents applied in the processes revealed exclude, however, any technical utility, of the processes described.
U.S. patent specification No. 4,614,718 does not relate to esters of glycosides but to sugar or sugar alcohol esters of higher fatty acids.
The PCT application having international publication No. WO 86/05186 does not relate to esters of glycosides but to a process wherein the starting material has only one free hydroxy group.
U.S. patent specification No. 2,759,922 relates to a process for preparing diesters, triesters and tetraesters of glycosides. Said patent does not describe the preparation of pure monoesters of glycosides. No enzymatic reactions are described in said patent.
German Offenlegungsschrift No. 2,360,368 relates to esters of polyglycosides having a degree of glycosidation of from 1.1 to 4. No enzymatic reactions are described in said Offenlegungsschrift.
One object of this invention is to provide novel compounds.
A further object of this invention is to provide surfactants having superior effects.
A still further object of this invention is to provide surfactants which have superior effects when used in detergents.
A further object of this invention is to provide cleaning agent compositions with better cleaning effects.
A still further object of this invention is to provide a process for preparing monoesters of glycosides.
A still further object of this invention is to provide monoesters of glycosides of monosaccharides.